The present invention relates to a method and apparatus for making high frequency measurements of super cooled system boards for the purposes of testing and/or implementation of engineering changes. More specifically, the present invention relates to a probing system for super cooled system boards by which moisture condensation and corrosion formation on the test site are avoided.
In the testing of large systems during the initial bring up and including debugging of system hardware, special modifications are typically made to the product. A metal stiffener used to support the large system boards is machined so that an open access is provided to e.g., pins of a Device Under Test (DUT), such as a Multi Chip Module (MCM), as well as to other points of interest. A method of measuring system operations utilizing holes drilled through a probe template made of an insulating material offers a full range of interconnections at all signal locations and selected ground or voltage reference locations of the DUT.
With the ever increasing operational speeds of computer systems, including mainframes, it is becoming more and more difficult to provide accurate measurements of operational parameters such as switching noise and signal integrity, jitter measurements, measurements of differential signals, and differential measurements of voltage to ground disturbances. To achieve higher operational speeds, future systems require that the temperature of the electronics"" operational point be reduced to near zero degrees C and below. Any testing with one side of a system at extremely low temperatures and the other side in an exposed room environment will cause condensation to form. This condensation will, over a period of time, cause corrosion of exposed metal interface connections. This is permissible in a dedicated system that will be scrapped, but not for machines that are to be used over long periods of time.
S/390 and IBM are registered trademarks of International Business Machines Corporation, Armonk, N.Y., U.S.A. and Lotus is a registered trademark of its subsidiary Lotus Development Corporation, an independent subsidiary of International Business Machines Corporation, Armonk, N.Y. Other names may be registered trademarks or product names of International Business Machines Corporation or other companies.
A probe test assembly according to the present invention which prevents condensation from forming on a Device Under Test (DUT) cooled to a temperature approaching 0xc3xa2C. or even less than 0xc3xa2C. includes a heat conducting probe plate mounted on one side of a large system board on the opposite side of which the DUT is mounted, with pins of the DUT extending into openings in the probe plate. Electrical resistance heaters are secured in heat-conducting relationship on the probe plate, which conducts the heat to the large system board and to the DUT, thereby raising the temperature of the pin side of the board above a level at which condensation forms. A large recess formed in the underside of the probe plate defines with the large system board a chamber which is pressurized by desiccated air is fed under pressure through passages in heat transfer relationship with the probe plate. Desiccated air under pressure is also fed directly to a space between the large system board and the DUT. Ground pins extend from openings in the probe plate to grounding pad locations at openings in the large system board. A non-conductive pattern plate having openings in alignment with the openings in the probe plate is space above the probe plate, and electric test probes are inserted through the aligned openings in the pattern plate and the probe plate to the openings in the large system board receiving the pins of the DUT. In view of the foregoing, the probe test assembly of the present invention provides for testing of DUT""s which is non-permanent, non-destructive and free from condensation.
In an alternate embodiment, the pattern plate is omitted in favor of a conductive intermediate plate space above the probe plate and a non-conductive contact plate spaced above the intermediate plate. Both the intermediate plate and the contact plate have openings aligned with the openings in the probe plate. Ground pin connections between the contact plate and grounding pad locations at openings in the large system board are made either by ground pins each extending all of the way from the contact board to the large system board or by a first set of grounding pins extending from the contact plate to the intermediate plate and a second set of grounding pins extending from the probe plate to the large system board. Signal pins extend from openings in the large system board, through openings in the probe plate and the intermediate plate, all the way to the contact plate, thereby transferring contact points for the DUT from a confined area of the large system board to the contact plate, which is unconfined. A multipin connector connected to the signal pin receiving openings of the contact plate can be mounted on the contact plate, so that the probe test assembly can be connected to a computer.